fix(health checker): collect DC from gossip info

This commit ensures that the DC information is correctly parsed and collected, even when it
appears after other data like schema, IP, or status.
Previously, the parser would miss this information due to its location, but this change fixes
that issue.

Author: juliayakovlev

sdcm/cluster.py

@@ -2882,7 +2882,7 @@ def get_gossip_info(self) -> dict[BaseNode, dict]:
             elif line.startswith('DC:'):
                 dc = line.replace('DC:', '').split(',')[0]
 
-            if schema and ip and status:
+            if schema and ip and status and dc:
                 if node := node_ip_map.get(ip):
                     gossip_node_schemas[node] = {'schema': schema, 'status': status, 'dc': dc}
                 elif status in self.GOSSIP_STATUSES_FILTER_OUT: